Seuret-Hernández Halis Yenis, Morera-Boado Cercis
Centro de Investigaciones Químicas, IICBA, Universidad Autónoma del Estado de Morelos, Cuernavaca, 62209, Morelos, Mexico.
Cátedra Conahcyt-Centro de Investigaciones Químicas, IICBA, Universidad Autónoma del Estado de Morelos, Cuernavaca, 62209, Morelos, Mexico.
J Phys Chem A. 2023 Aug 17;127(32):6697-6710. doi: 10.1021/acs.jpca.3c02368. Epub 2023 Aug 3.
This work presents a theoretical detailed analysis of the surface-enhanced Raman spectroscopy (SERS) of the pyridine-MN (M, N = Ag, Cu) tetrahedral () clusters considering two binding positions: vertex (V) and surface (S). In addition to the well-known monometallic structure, we added two different bimetallic Ag-Cu compositions, named and geometries. Density functional methodology with the use of BP86 and CAM-B3LYP exchange-correlation functionals (XCs) and LANL2DZ pseudopotential has been employed for analyzing the electronic structure and geometries, the chemical static (CHEM), and resonant Raman mechanisms (RR): charge transfer RR-CT and intracluster excitation RR-CR. The static CHEM mechanism shows an increase in the enhancement factors (EFs) of Py-V concerning Py-S positions, which can also be distinguished by the averaged adsorption energies and bond polarizabilities. The static SERS response for Cu-Py-V junction is from 5 to 10 times greater than Ag-Py-V EFs and up to 28 times greater than Py-S complexes. For the static Raman, we found that the analyses of ν and ν normal modes are related to the EF changes and allow us to distinguish V from S complexes. The TDDFT calculations show striking differences between BP86 and CAM-B3LYP XCs analyzed spectra, and CAM-B3LYP granted a clear distinction between V and S for the location of CT-type transitions. In addition, important differences were obtained from the analysis of the charge transfer excitations between both XCs. Resonant Raman calculations evidenced significant enhancements for RR-CT and RR-CR as compared to the static enhancements, and RR-CT can be distinguished from the RR-CR mechanism, while specific normal modes help to differentiate the vertex from the surface Py-junction. Bimetallic Ag-Cu nanostructures represent promising choices for SERS substrates, showing EFs higher than those of monometallic Ag.
这项工作对吡啶-MN（M、N = Ag、Cu）四面体（）簇的表面增强拉曼光谱（SERS）进行了理论上的详细分析，考虑了两个结合位置：顶点（V）和表面（S）。除了众所周知的单金属结构外，我们还添加了两种不同的双金属Ag-Cu组成，分别命名为和几何结构。采用密度泛函方法，使用BP86和CAM-B3LYP交换相关泛函（XCs）以及LANL2DZ赝势来分析电子结构和几何结构、化学静态（CHEM）以及共振拉曼机制（RR）：电荷转移RR-CT和团簇内激发RR-CR。静态CHEM机制表明，与Py-S位置相比，Py-V的增强因子（EFs）有所增加，这也可以通过平均吸附能和键极化率来区分。Cu-Py-V结的静态SERS响应比Ag-Py-V的EFs大5到10倍，比Py-S配合物大28倍。对于静态拉曼，我们发现对ν和ν简正模式的分析与EF变化有关，并且能让我们区分V和S配合物。含时密度泛函理论（TDDFT）计算表明，BP86和CAM-B3LYP XCs分析的光谱之间存在显著差异，并且CAM-B3LYP对于CT型跃迁的位置能够清晰区分V和S。此外，通过对两种XCs之间电荷转移激发的分析获得了重要差异。共振拉曼计算表明，与静态增强相比，RR-CT和RR-CR有显著增强，并且RR-CT可以与RR-CR机制区分开来，同时特定的简正模式有助于区分顶点和表面的Py结。双金属Ag-Cu纳米结构是SERS基底的有前景的选择，其EFs高于单金属Ag。
